Water entering watersheds from land and through drains can have a significant impact on the health of aquatic habitats. Runoff for example, can carry with it topsoil, grease and oil from roads, fertilizers, pesticides and other pollutants that may result in harmful algal blooms or direct mortality of fish.

The coho salmon is an iconic species that has been experiencing severely high rates of premature adult mortality prior to spawning in many urban stream networks in north-western America. This has been attributed to increased rainfall and storm water runoff; the salmon's migration to freshwater spawning habitats coinciding with runoff entering rivers, lakes and streams. An important question for conservation has been how to best mitigate these impacts and prevent such fish kills? Part of the problem has been lack of specific knowledge on which contaminants are responsible for the mortality and which controls could be employed to prevent it.

In an experimental study, Spromberg et al. have shown for the first time that untreated highway water runoff following storm events (and not conventional urban storm water which contains metals and petroleum hydrocarbons) was the culprit for coho salmon mortality. Importantly deaths were prevented when the highway runoff was treated with soil infiltration – a conventional green storm water infrastructure technology. In a recent related study (McIntyre et al. 2015) the authors and collaborators also found that juvenile coho salmon and their macroinvertebrate prey could be protected by this relatively inexpensive type of green storm water infrastructure (GSI) making it a promising innovation for protecting urban freshwater ecosystems.

How readily can this promising GSI be implemented across enough watersheds to make it effective in north-western America and in impacted watersheds elsewhere? The widespread use of GSI science is still in its infancy. Key questions include understanding the amount and spatial scale of treatment that would be required to prevent coho salmon deaths in natural systems. They are likely to be one of many management innovations. Because the authors have identified a link between the non-point source pollution and mortality syndrome, their research could advance future work on habitat quality indicators and vulnerability in North America and elsewhere. Under future population growth and road development, freshwater life could be at even greater risk. Mapping vulnerable habitats now and in the future would represent a first step towards generalising these findings beyond their sentinel species and system. Isolating the precise chemicals that cause stress and mortality would also help in developing future management options.